Asymptomatic Bacteriuria

Background

• Asymptomatic bacteriuria (ASB) refers to the isolation of a defined minimum quantity of bacteria in a urine specimen from a person without signs or symptoms of a urinary tract infection (UTI).
• ASB prevalence in women is associated with sexual activity, and increases with age. ASB is also more common in women with diabetes, elderly patients, patients on hemodialysis, and patients with urinary catheters and bladder dysfunction.
• ASB is rare in young men with a normal genitourinary tract, but prevalence increases in elderly men.
• Despite increased prevalence in many populations, treatment of ASB is usually recommended for only 2 subsets of patients
  • Pregnant women, because ASB may be associated with a small increased risk of adverse outcomes including pyelonephritis, preterm delivery, and low birth weight in infants.
  • Patients undergoing urologic procedures, because ASB is associated with complications such as bacteremia and sepsis.

Evaluation

• Urine culture is the appropriate screening test when indicated.
• Bacterial concentration and specimen type needed for diagnosis varies with patient population.
• Infectious Diseases Society of America (IDSA) and European Association of Urology (EAU) define ASB as:
  • ≥ 10⁵ colony-forming (CF) units/mL of a single bacterial strain isolated from 2 consecutive voided urine specimens in asymptomatic women
  • ≥ 10⁵ CF units/mL of a single bacterial species isolated from a single urine specimen in asymptomatic men
  • ≥ 10² CF units/mL of a single bacterial species from a single catheterized specimen
• Pyuria is common with ASB, and is not an indication for treatment.
• IDSA and EAU recommend routine screening for ASB in 2 subsets of patients
  • For pregnant women, screen once early in pregnancy (Strong recommendation).
  • For patients undergoing urologic procedures that may interfere with the urinary tract, culture should be obtained such that results will be available to direct therapy prior to the procedure (Strong recommendation).

Management

• Treatment is recommended for pregnant women and patients undergoing urological procedures with potential for mucosal bleeding (Strong recommendation).
  • In pregnant women with asymptomatic bacteriuria:
    • Optimal duration of therapy is not known, but IDSA recommends 4-7 day course, same as treatment for symptomatic cystitis.
    • No specific empiric therapy has been shown to be superior to another for the treatment of ASB in pregnancy. Common options include penicillins, cephalosporins, or fosfomycin.
    • Definitive therapy should be directed at isolated organism.
    • Follow-up cultures should be obtained to ensure resolution.
  • In patients undergoing urologic procedures, treatment should begin before the procedure, and directed at the isolated organism.
• The necessity of screening and treatment in immunocompromised hosts (such as renal transplant recipients and neutropenic patients) is not yet established.
• In other populations, ASB may be associated with an increased risk of symptomatic infections. However, treatment has not been clearly associated with improved outcomes, and is therefore not recommended.